Text Telephony (TTY) has been used by hearing and speech impaired people for many years over the plain old telephone system (POTS). In recent years, TTY has been used over analog cellular phones using the advanced mobile phone system (AMPS) standard. In general, TTY devices use Baudot codes to signal text from one user to another over the regular voice channel.
Digital cellular phones improve network capacity by using voice coders that encode the voice at a mobile phone and decode it later in the network. Unfortunately, voice coders interfere with the TTY Baudot codes. Furthermore, additional functionality needs to be implemented in both mobile handsets and the network infrastructure in order to support TTY on digital networks.
TTY mobile device systems for the global system for mobile communications (GSM) standard exist. GSM, originally “Groupe de travail Spéciale pour les services Mobiles”, is a standard for digital cellular communications that is currently in the process of being adopted by over 60 countries. The GSM standard currently uses the 900 MHz and 1800 MHz bands, as well as 1900 MHz bands in some countries. Similar implementation architecture exists for the other digital cellular networks.
TTY mobile device systems include mobile devices capable of signaling to a wireless network if the device does or does not support TTY at call setup. This notification is generally accomplished using a TTY bearer bit. The TTY bearer bit ensures that each TTY call is routed to the correct decoder/encoder in the network. A TTY mode switch in the mobile device must be present in order to minimize the number of calls being routed through the CTM decoder/TTY encoder. It is stated in Section 255 of the Telecom Act that in the United States manufacturers are required to provide a “usable” solution for users and not just a solution for 911 emergency calls. There are many possible solutions for the mode switch, but the selected solution should minimize the number of normal voice calls with the TTY bearer bit enabled and make easy access for the TTY user to enable the TTY mode switch.
Conventional TTY mobile device systems require users to enter a code or some other manual technique to indicate that a TTY device is connected to the mobile device or that the mobile device needs to be in TTY mode. Manually informing the mobile device of the TTY connection or TTY mode is cumbersome and time consuming. Further, the manual technique must be repeatedly used if the mobile device frequently uses both TTY and non-TTY communications.
Thus, there is a need for a system for and method of detecting a connection of a text telephony (TTY) device to a mobile phone. Further, there is a need to detect the presence of a TTY cable connection upon its attachment such that the mobile device can communicate a TTY bearer bit to its wireless network. Yet further, there is a need to enable the TTY bearer bit dynamically.